Optical disk and method of fabricating the same

ABSTRACT

An optical disk and a method of fabricating the optical disk capable of improving the signal quality and the productivity are disclosed. The optical disk includes a plurality of reflective layers stacked on a substrate, amorphous layers formed among the reflective layers which include a small amount of oxide therein, a recording layer, formed on the reflective layer, for recording information, and a cover layer formed on the recording layer.

[0001] This application claims the benefit of the Korean ApplicationNos. P2001-23387 and P2001-32109 filed on Apr. 30, 2001 and Jun. 8,2001, respectively, which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an optical disk and a method offabricating the optical disk.

[0004] 2. Discussion of the Related Art

[0005] Generally, in a phase-change type optical disk, recordedinformation is erased in a manner that a local area of a recording layeris heated and melted by irradiating a laser beam onto the area, and thenan amorphous mark is made on a crystal matrix through a quick coolingusing a disk structure designed to have a quick heat diffusion.

[0006] The phase-change type optical disk having the above-describedprinciple is typically composed of a simple four-layer film, i.e., afour-layer film structure in that a lower dielectric layer, a recordinglayer, an upper dielectric layer, and a reflective layer are stacked ona substrate.

[0007] The optical disk may have a structure composed of more than fourlayers. In this case, any additional layers may be formed among thebasic four layers. At this time, the reflective layer is formed at theend.

[0008] This structure formed in the above-described order is called anormal stacking structure.

[0009] Recently, with the development of a high-density recordablemedium, there is a tendency to increase the numerical aperture of anobject lens of an optical pickup and to bring the wavelength of arecording optical source into being shorter in an optical recordingapparatus.

[0010] In this case, as the numerical aperture is increased, the workingdistance between the object lens and the recording layer of the opticalrecording medium becomes shorter. Accordingly, the thickness of atransparent substrate that exists in the middle of the optical sourceand the recording layer should be reduced.

[0011] Consequently, the role of the substrate has progressed from itsown function for supporting the thin film in the previous normalstacking structure to a thin cover layer for covering the multi-layerthin film that exists on the path through which the laser passes.

[0012] Also, in case of increasing the numerical aperture of the lens, acoma aberration due to a tilt that is one of mechanical fluctuations ofthe disc is greatly increased in proportion to the cube of the numericalaperture. Especially, since the coma aberration becomes greater as thethickness of the substrate positioned on the path through which theincident laser beam passes becomes thicker, the thickness of thesubstrate should be reduced.

[0013] In this case, the stacking order of the thin film is a reversedstacking order in that the reflective layer is first stacked on thecontrary to the normal stacking order in that the reflective layer islast stacked.

[0014] In such a reversed stacking structure, the reflective layer isfirst formed on the substrate, other layers are stacked, and then acover layer is formed over the upper part of the formed structure.Accordingly, the signal characteristics of the optical disk is greatlyinfluenced by the micro structure of the surface of the reflective layerthat is the thin film positioned on the lowest part of the structure.Especially, a focus error signal becomes greater in a dynamic drivingstate of the medium, and this causes a medium noise to be increased.

[0015] As a result, a surface roughness of the recording medium thatcauses the medium noise should be lowered.

[0016] In order to lower the surface roughness of the reflective layer,an ion beam sputtering method has been proposed instead of a typicalsputtering method. However, this method has the drawbacks in that thetime required for the whole process is too long to be suitable for massproduction.

SUMMARY OF THE INVENTION

[0017] Accordingly, the present invention is directed to an optical diskand a method of fabricating the same that substantially obviate one ormore problems due to limitations and disadvantages of the related art.

[0018] An object of the present invention is to provide an optical diskand a method of fabricating the same that can provide a superior signalquality by reducing the surface roughness of a reflective layer.

[0019] Another object of the present invention is to provide an opticaldisk and a method of fabricating the same that has a superiorproductivity with a simple process.

[0020] Additional advantages, objects, and features of the inventionwill be set forth in part in the description which follows and in partwill become apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

[0021] To achieve these objects and other advantages and in accordancewith the purpose of the invention, as embodied and broadly describedherein, an optical disk includes a substrate, a plurality of reflectivelayers stacked on the substrate, amorphous layers formed among therespective reflective layers, a recording layer, formed on thereflective layer, for recording information, and a cover layer formed onthe recording layer.

[0022] Here, the reflective layer is made of a mixture obtained byadding SiO₂ to any one of Al, Al alloy, Ag, and Ag alloy, and adielectric layer composed of ZnS—SiO₂ is formed on upper and lower partsof the recording layer.

[0023] The amorphous layer is made of any one of Si-oxide, Al-oxide,Ti-oxide, Cr-oxide and ZnS—siO₂ or made of either of a Ge—Sb—Te typealloy thin film and a Ag—In—Sb—Te type alloy thin film.

[0024] In another aspect of the present invention, a method offabricating an optical disk includes the steps of forming by turns afirst reflective layer and an amorphous layer on a substrate, forming asecond reflective layer on the amorphous layer, forming by turns anupper dielectric layer, a recording layer, and a lower dielectric layeron the second recording layer, and forming a cover layer on the lowerdielectric layer.

[0025] At this time, the step of forming by turns the first reflectivelayer and the amorphous layer on the substrate may be repeated accordingto circumstances.

[0026] According to the present invention fabricated as described above,the surface roughness of the reflective layer is greatly reduced, andthus an optical recording medium having a superior signal quality can beobtained. Also, a multi-layer reflective layer can be formed by theexisting sputtering method, and its productivity is superior.

[0027] It is to be understood that both the foregoing generaldescription and the following detailed description of the presentinvention are exemplary and explanatory and are intended to providefurther explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings, which are included to provide afurther understanding of the invention and are incorporated in andconstitute a part of this application, illustrate embodiment(s) of theinvention and together with the description serve to explain theprinciple of the invention. In the drawings:

[0029]FIG. 1 is a graph illustrating the surface roughness on interfacesof the respective layers during a normal stacking.

[0030]FIG. 2 is a graph illustrating the surface roughness on interfacesof the respective layers during a reversed stacking.

[0031]FIGS. 3A and 3B are cross-sectional views illustrating thestructure of an optical disk according to first and second embodimentsof the present invention.

[0032]FIG. 4 is a graph illustrating the surface roughness according toaddition of SiO₂ to the reflective layer.

[0033]FIG. 5 is a graph illustrating the surface roughness according tothe thickness of the reflective layer of the optical disk.

[0034]FIG. 6 is a graph illustrating the comparative surface roughnessof the reflective layer having an amorphous layer inserted therein andthe reflective layer having no amorphous layer.

[0035]FIG. 7 is a TEM image showing the effect of the addition of SiO₂into Al-matrix.

[0036] DETAILED DESCRIPTION OF THE INVENTION

[0037] Reference will now be made in detail to the preferred embodimentsof the present invention, examples of which are illustrated in theaccompanying drawings. Wherever possible, the same reference numberswill be used throughout the drawings to refer to the same or like parts.

[0038]FIG. 1 is a graph illustrating the surface roughness on interfacesof the respective layers during a normal stacking, and FIG. 2 is a graphillustrating the surface roughness on interfaces of the respectivelayers during a reversed stacking.

[0039] In case of the normal stacking as shown in FIG. 1, the mainreflected signal is detected from the upper and lower parts of therecording layer during the recording/reproducing operation, and thus thegreat surface roughness of the recording layer does not affect thesignal characteristics of the recording medium.

[0040] On the contrary, in case of the reversed stacking as shown inFIG. 2, the great surface roughness of the recording layer due to thesurface roughness of the reflective layer causes the generation of noiseduring the detection of the recorded/reproduced signal, and this greatlydeteriorates the signal.

[0041] Specifically, the great surface roughness of the recording layerdue to the surface roughness of the reflective layer causes a focuserror signal in the dynamic driving state of the optical recordingmedium, and this causes the noise of the medium to be increased.

[0042] The present invention improves the surface roughness of thereflective layer appearing in the reversed stacking structure of theoptical disk by forming at least one amorphous layer among thereflective layers.

[0043] That is, the present invention is directed not to form thereflective layer made of Al, etc., as a single layer as in theconventional manner, but to form one or more intermediate layers havingan amorphous structure among the reflective layers to lower the surfaceroughness of the reflective layer.

[0044]FIGS. 3A and 3B are cross-sectional views illustrating thestructure of an optical disk according to first and second embodimentsof the present invention. FIG. 3A shows the embodiment employing oneamorphous layer formed between the reflective layers, and FIG. 3B showsthe embodiment employing a plurality of amorphous layers formed amongthe reflective layers.

[0045] According to the present invention, as shown in FIGS. 3A and 3B,a plurality of reflective layers 11 are stacked on a polycarbonatesubstrate 10 having a thickness of about 1.1 mm, and amorphous layer(s)12 is(are) formed among the respective reflective layers 11. A recordinglayer 13 for recording information is formed on the upper reflectivelayer 11, and a cover layer 14 with a thickness of about 0.1˜0.12 mm isformed on the recording layer 13.

[0046] Here, the reflective layer 11 is made of a mixture obtained byadding SiO₂ to any one of Al, Al alloy, Ag, and Ag alloy in the ratio of0.1˜10 mol %, and its thickness is in the range of 100˜1000 Å. This isbased on the characteristics in that the larger the amount of added SiO₂is added, the smaller the surface roughness of the reflective layer 11becomes.

[0047] At this time, in case of forming one amorphous layer 12 betweenthe two reflective layers 11 according to the first embodiment of thepresent invention, the thickness of the respective reflective layers 11is set to about 500 Å, and in case of forming a plurality of amorphouslayers 12 among the reflective layers 11 according to the secondembodiment of the present invention, the thickness of the respectivereflective layers is set to about 330 Å.

[0048] Also, the amorphous layer 12 formed between the reflective layers11 is made of any one of Si-oxide, Al-oxide, Ti-oxide, Cr-oxide,ZnS—siO₂, and mixtures thereof, or made of either a Ge—Sb—Te type alloythin film or a Ag—In—Sb—Te type alloy thin film. Its thickness is in therange of about 20˜40 Å, and in the embodiments of the present invention,its thickness is set to about 30 Å.

[0049] The recording layer 13 is made of a Sb—Te—Ge alloy or anAg—In—Sb—Te type alloy, and its thickness is in the range of about100˜300 Å.

[0050] On the upper and lower parts of the recording layer 13 are formeddielectric layers 15. Under certain circumstances, the dielectric layer15 may be formed. The dielectric layer 15 is made of one among ZnS—SiO₂,SiO₂, SiN, (Zr_(x)Ce_(1-x))_(y)O_(1-y), AlN, and Al₂O₃. The thickness ofthe dielectric layer 15 b formed on the upper part of the recordinglayer 13 is in the range of about 500˜3000 Å, and the thickness of thedielectric layer 15 a formed on the lower part of the recording layer 13is in the range of about 100˜500 Å.

[0051] The cover layer 14 may be made of UV curing resin, and itsthickness is in the range of 0.1˜0.12 mm or is bounded less than 0.1 mmthickness polycarbonate film with UV curing resin.

[0052] Now, the method of fabricating the optical disk according to thepresent invention will be explained.

[0053] The optical disk fabricating method according to the presentinvention uses a magnetron sputtering deposition. Specifically, Ar thatis an inert gas is filled in a vacuum chamber (not illustrated), andionized by applying a high DC or RF (radio frequency) voltage to atarget that is the source of the thin film. Then, the thin films areformed using ions emitted by the collision of the ionized Ar with thetarget.

[0054] According to the above magnetron sputtering deposition, the thinfilms of not only metals but also dielectric materials can be easilyformed. Also, since the process is performed using a high-level energy,the adhesive strength of the thin film becomes great. Also, since itsstep coverage is superior, a uniform thin film can be formed.

[0055] First, a first reflective layer 11 a and an amorphous layer 12are formed by turns on a substrate 10, and then a second reflectivelayer 11 b is formed on the amorphous layer 12.

[0056] At this time, the first and second reflective layers 11 a and 11b are deposited by sputtering a target in which a metal and SiO₂ aremixed together, i.e., either of an Al—SiO₂ target and an Ag—SiO₂ target,or by co-sputtering an SiO₂ target and either of an Al target and an Agtarget.

[0057] Here, in case of inserting several amorphous layers 12 as shownin FIG. 3b, the above-described process is repeatedly performed to formby turns a second reflective layer 11 b and a second amorphous layer 12b on a first amorphous layer 12 a, and to form a third reflective layer11 c on the second amorphous layer 12 b.

[0058] Thereafter, a upper dielectric layer 15 a, a recording layer 15,and an lower dielectric layer 15 b are formed by turns on the upperreflective layer 11 c, and then a cover layer 14 is formed thereon witha thickness of about 0.1˜0.12 mm using a UV curing resin to produce anoptical disk.

[0059]FIG. 4 and 7 illustrate the resulting effect of surface roughnessaccording to the addition of SiO₂ into the Al reflective layer. FIG. 4shows that the surface roughness becomes smaller as SiO₂ is added.

[0060] The reason why the surface roughness of the reflective layer isreduced is that SiO₂ has a pinning role of grain boundary movement. So aprecipitated Sio₂ suppresses a columnar growth of Al possibly due todrag force acting on grain boundary.

[0061]FIG. 5 is a graph illustrating the surface roughness according tothe thickness of the reflective layer of the optical disk. As shown inFIG. 5, the surface roughness is linearly reduced as the thickness ofthe reflective layer becomes smaller.

[0062] According to the present invention, a single reflective layer isnot formed, but a plurality of unit reflective layers having a smallthickness are stacked with amorphous layers having a small thicknessinserted therein, respectively, so that the whole thickness of thereflective layer is constant, and the surface roughness is improved.

[0063]FIG. 6 is a graph illustrating the comparative surface roughnessof the reflective layer having an amorphous layer inserted therein andthe reflective layer having no amorphous layer inserted therein.

[0064] Here, “Type 1” indicates a case that one amorphous layer of about50 Å is inserted between two reflective layers of about 1000 Å. “Type 2”indicates a case that two amorphous layers of about 30 Å are insertedamong reflective layers of about 1000 Å. Also, four kinds of amorphouslayers are used in comparing the surface roughness of the reflectivelayers.

[0065] As shown in FIG. 6, the surface roughness of the reflective layerof 1000 Å that has no amorphous layer inserted therein is about 23 Å. Onthe contrary, the surface roughness of the reflective layer having anamorphous layer inserted as an intermediate layer is abruptly decreasedthough there is a difference according to the kind of the amorphouslayers.

[0066] The reason why the surface roughness of the reflective layer isreduced is that a column structure is formed as the reflective layer isgrown, and a great column is formed due to a mutual combination amongcolumns to increase the surface roughness.

[0067] That is, in view of the grain growth of a general phase changetheory, the great column structure causes the surface roughness to beincreased.

[0068] On the contrary, in case of inserting the amorphous layer betweenthe reflective layers, the column growth due to the continuous growth isdisturbed, and a new crystalline layer is formed on the surface of theamorphous layer, so that the final surface roughness of the reflectivelayer is greatly reduced.

[0069] As described above, the optical disk according to the presentinvention has the advantages in that the surface roughness of thereflective layer is reduced through insertion of an amorphous layer intothe reflective layers, and thus the optical disk has a superior signalquality. Also, according to the optical disk fabricating methodaccording to the present invention, multiple reflective layers can beformed by the existing sputtering method with a superior productivity.

[0070] It will be apparent to those skilled in the art than variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. An optical disk comprising: a substrate; aplurality of reflective layers stacked on the substrate; amorphouslayers formed among the reflective layers; a recording layer, formed onthe reflective layer, for recording information; and a cover layerformed on the recording layer.
 2. The optical disk as claimed in claim1, wherein the reflective layer is made of a mixture obtained by addingan oxide to any one selected from the group consisting of Al, Al alloy,Ag, and Ag alloy.
 3. The optical disk as claimed in claim 2, wherein theoxide is SiO₂.
 4. The optical disk as claimed in claim 2, wherein theadding ratio of the oxide is in the range of 0.1˜10 mol %.
 5. Theoptical disk as claimed in claim 1, wherein the thickness of thereflective layer is in the range of 100˜1000 Å.
 6. The optical disk asclaimed in claim 1, wherein the amorphous layer is made of a materialselected from the group consisting of Si-oxide, Al-oxide, Ti-oxide,Cr-oxide, and ZnS—siO₂.
 7. The optical disk as claimed in claim 1,wherein the amorphous layer is made of either of a Ge—Sb—Te type alloythin film and an Ag—In—Sb—Te type alloy thin film.
 8. The optical diskas claimed in claim 1, wherein the thickness of the amorphous layer isin the range of 10˜50 Å.
 9. The optical disk as claimed in claim 1,wherein the recording layer is made of either of a Sb—Te—Ge alloy and anAg—In—Sb—Te type alloy, and its thickness is in the range of 100˜300 Å.10. The optical disk as claimed in claim 1, further comprising upper andlower dielectric layers formed on upper and lower parts of the recordinglayer, respectively.
 11. The optical disk as claimed in claim 10,wherein the upper and lower dielectric layers are made of one selectedfrom the group consisting of ZnS—SiO₂, SiO₂, SiN,(Zr_(x)Ce_(1-x))_(y)O_(1-y), AlN, and Al₂O₃.
 12. The optical disk asclaimed in claim 10, wherein the thickness of the upper dielectric layeris in the range of 100˜300 Å, and the thickness of the lower dielectriclayer is in the range of 500˜3000 Å.
 13. The optical disk as claimed inclaim 1, wherein the cover layer is made of an UV curing resin, and itsthickness is in the range of 0.09˜0.12 mm.
 14. A method of fabricatingan optical disk comprising the steps of: forming by turns a firstreflective layer and an amorphous layer on a substrate; forming a secondreflective layer on the amorphous layer; forming by turns an upperdielectric layer, a recording layer, and a lower dielectric layer on arecording layer; and forming a cover layer on the lower dielectriclayer.
 15. The method as claimed in claim 14, wherein the step offorming by turns the first reflective layer and the dielectric layer onthe substrate is repeatedly performed.
 16. The method as claimed inclaim 14, wherein the first and second reflective layers are formed bysimultaneously sputtering a metal and an oxide.
 17. The method asclaimed in claim 16, wherein the sputtering is performed using a targetin which the metal and the oxide are mixed together.
 18. The method asclaimed in claim 17, wherein the target in which the metal and the oxideare mixed is either of an Al—SiO₂ target and an Ag—SiO₂ target.
 19. Themethod as claimed in claim 16, wherein the sputtering is performed usinga metal target and an oxide target.
 20. The method as claimed in claim19, wherein the metal target is any one of an Al target and an Agtarget, and the oxide target is a SiO₂ target.